Increment Detection Thresholds Research Articles

Linking perceived to physical contrast: Comparing results from discrimination and difference-scaling experiments.

Psychophysical approaches that allow us to estimate how perceived stimulus intensity is linked to physical intensity are import tools for studying nonlinear transformations of visual signals within different visual pathways. Here, we investigated how stimulus contrast is encoded in achromatic and chromatic pathways using simple grating stimuli. We compared two experimental approaches to this question: contrast discrimination (increment detection thresholds measured on contrast pedestals) and the maximum likelihood difference scaling (MLDS) approach introduced by Maloney and Yang (2003). The results of both experiments are expressed using simple models that include a transducer function mapping physical contrast to an internal signal the observer uses in making judgments, and an estimate of the variability of this representation (internal “noise”). We found that the transducers derived from both experiments have a similar form, but occupy different ranges of physical contrast in different stimulus conditions, reflecting difference in contrast sensitivity. This is consistent with past discrimination results, and in the difference-scaling case provides new evidence supporting the idea that suprathreshold chromatic and achromatic contrast are processed similarly, once differences in contrast sensitivity are taken into account. Model estimates of internal noise were higher in the difference-scaling experiment than the discrimination experiment, a finding we attribute to a difference in task complexity. Finally, we fit an alternative version of the MLDS model in which internal noise increased with response level. This alternative was no better at predicting holdout data in a cross-validation analysis than the original constant-variance model.

The effect of simultaneous flickering light stimulation on global form and motion perception thresholds

The question regarding the exact function of the primary visual cortex (V1) in vision has been around ever since the description of residual vision after damage to this cortical area by Riddoch in 1917. In 2002, Schoenfeld and colleagues proposed that V1 can be saturated by flashes of light, by which the function of V1-bypassing visual pathways can be “unmasked”. The Schoenfeld group found that light flashes applied on stimulus onset led to the elevation of brightness increment detection thresholds, but left motion detection thresholds unaltered. Although the proposed method (i.e. the use of light flashes to induce refractoriness in V1) could be a simple, cheap and elegant way of exploring V1 functions, no study has followed up on this. Therefore it is not known if it works at all with other types of stimuli. For that reason, we decided to revisit the idea in a modified form. Global form and motion perception thresholds were assessed with static Glass pattern stimuli and random dot kinematograms, with and without 12Hz flickering light stimulation. Global motion thresholds were almost unaltered by flickering stimulation, while a significant threshold elevation was caused in the global form perception task. The strongest conclusion allowed by our data is that simultaneous flickering photostimulation elevates global form perception thresholds but not global motion perception thresholds. This is in some way related to the refractoriness generated in an unsatisfactorily defined part of V1. We suggest that this does not necessarily reflect the activity of V1-bypassing pathways, and propose that the application of light flashes is a method that deserves more attention in the exploration of the V1-dependent and independent elements of visual consciousness in human subjects.

Relative contributions of on- and off-frequency spectral cues in increment detection

Increment detection is often used as a measure of intensity resolution, where a listener detects a brief increment in intensity in a longer duration stimulus. Recent findings suggest that listeners rely on multiple cues rather than on-frequency energy cues. The relative contributions of on- and off-frequency cues are evaluated in five normal-hearing young adults. Detection thresholds for a 50-ms increment added in the middle of a 450-ms, 1000-Hz pedestal were obtained in quiet, telegraph noise (TN), and notched-noise (NN) conditions. The pedestal level was 60 dB SPL. NN stimuli were generated by filtering TN while keeping the notch geometrically centered at 1000 Hz. The NN-notches were also varied by increasing the notch-width unevenly on either side of the center frequency. The low-frequency cutoffs of the NN-notches were 125, 250, 500, and 750 Hz while the high-frequency cutoffs were 1500, 2000, and 4000 Hz. Although the NN-notches were centered at 1000 Hz, increment detection thresholds were poorer in NN conditions than in quiet. Detection thresholds were similar in TN and NN with the narrowest notch conditions. Results suggest that listeners may rely on a decision process based on multichannel on- and off-frequency cues. [Supported by BU research and scholarship grant]

Auditory temporal-envelope processing in high-functioning children with Autism Spectrum Disorder

Individuals with Autism Spectrum Disorder (ASD) perform worse than controls when listening to speech in a temporally modulated noise (Alcántara, Weisblatt, Moore, & Bolton, 2004; Groen et al., 2009). The current study examined whether this is due to poor auditory temporal-envelope processing. Temporal modulation transfer functions were measured in 6 high-functioning children with ASD and 6 control listeners, using sinusoidal amplitude modulation of a broadband noise. Modulation-depth thresholds at low modulation rates were significantly higher for the ASD group than for the Control group, and generally higher at all modulation rates tested. Low-pass filter model estimates of temporal-envelope resolution and temporal-processing efficiency showed significant differences between the groups for modulation-depth threshold values at low modulation rates. Intensity increment-detection thresholds, measured on a subset of individuals in the ASD and Control groups, were not significantly different. The results are consistent with ASD individuals having reduced processing efficiency of temporal modulations. Possible neural mechanisms that might underlie these findings are discussed.

Relative effects of increment and pedestal duration on the detection of intensity increments.

The detection of a brief increment in the intensity of a longer duration pedestal is commonly used as a measure of intensity-resolution. Increment detection is known to improve with increasing duration of the increment and also with increasing duration of the pedestal, but the relative effects of these two parameters have not been explored in the same study. In several past studies of the effects of increment duration, pedestal duration was increased as increment duration increased. In the present study, increment and pedestal duration were independently manipulated. Increment-detection thresholds were determined for four subjects with normal-hearing using a 500- or 4000-Hz pedestal presented at 60 dB sound pressure level (SPL). Increment durations were 10, 20, 40, 80, 160, and 320 ms. Pedestal durations were 20, 40, 80, 160, and 320 ms. Each increment duration was combined with all pedestals of equal or greater duration. Multiple-regression analyses indicate that increment detection under these conditions is determined primarily by pedestal duration. Follow-up experiments ruled out effects of off-frequency listening or overshoot. The results suggest that effects of increment duration have been confounded by effects of pedestal duration in studies that co-varied increment and pedestal duration. Implications for models of temporal integration are discussed.

Effects of external noise on detection of intensity increments

The detection of an intensity increment in a longer duration sinusoid or pedestal is often used as a measure of intensity resolution, but the decision processes underlying this measure are poorly understood. Thresholds were obtained for detection of an increment in a 370-ms, 4-kHz pedestal in quiet or in noise to determine the relative contributions of background noise level and pedestal level, the effect of increment duration, and the effect of different noise spectra. Increment detection thresholds expressed in units of DeltaL[10 log(1+DeltaI/I)] decreased as pedestal levels increased. At low pedestal levels, increment detection was limited by the masking effect of the noise and was similar across noise conditions for pedestals of equal sensation level. At high pedestal levels, the noise had no effect and increment detection was determined by the pedestal level in dB SPL (sound pressure level). Increment detection improved with increasing increment duration and was altered less by a noise band above the pedestal/increment frequency than by a broadband noise that produced equal masking at the pedestal/increment frequency. The quadratic-compression model described by Neely and Jesteadt [(2005). Acta Acust. Acust. 91, 980-991] provided a better approximation to the data than a model based on excitation patterns.

A Psychophysical Evaluation of Spectral Enhancement

Listeners with sensorineural hearing loss have well-documented elevated hearing thresholds; reduced auditory dynamic ranges; and reduced spectral (or frequency) resolution that may reduce speech intelligibility, especially in the presence of competing sounds. Amplification and amplitude compression partially compensate for elevated thresholds and reduced dynamic ranges but do not remediate the loss in spectral resolution. Spectral-enhancement processing algorithms have been developed that putatively compensate for decreased spectral resolution by increasing the spectral contrast, or the peak-to-trough ratio, of the speech spectrum. Several implementations have been proposed, with mixed success. It is unclear whether the lack of strong success was due to specific implementation parameters or whether the concept of spectral enhancement is fundamentally flawed. The goal of this study was to resolve this ambiguity by testing the effects of spectral enhancement on detection and discrimination of simple, well-defined signals. To that end, groups of normal-hearing (NH) and hearing-impaired (HI) participants listened in 2 psychophysical experiments, including detection and frequency discrimination of narrowband noise signals in the presence of broadband noise. The NH and HI listeners showed an improved ability to detect and discriminate narrowband increments when there were spectral decrements (notches) surrounding the narrowband signals. Spectral enhancements restored increment detection thresholds to within the normal range when both energy and spectral-profile cues were available to listeners. When only spectral-profile cues were available for frequency discrimination tasks, performance improved for HI listeners, but not all HI listeners reached normal levels of discrimination. These results suggest that listeners are able to take advantage of the local improvement in signal-to-noise ratio provided by the spectral decrements.

Analysis of spectral shape in the barn owl auditory system

In a behavioral experiment, we investigated how efficiently barn owls (Tyto alba) could detect changes in the spectral profile of multi-component auditory signals with stochastic envelope patterns. Signals consisted of one or five bands of noise (bandwidth 4, 16, or 64 Hz each; center frequencies 1.02, 1.43, 2.0, 2.8, 3.92 kHz). We determined increment thresholds for the 2 kHz component for three conditions: single-band condition (only the 2 kHz component), all five noise bands with the envelope fluctuations of the bands being either correlated or uncorrelated. Noise bandwidth had no significant effect on increment detection. Increment thresholds for the different conditions, however, differed significantly. Thresholds in correlated conditions were generally the lowest of all conditions, whereas, thresholds in uncorrelated conditions mostly resulted in the highest thresholds. This can be interpreted as evidence for comodulation masking release in barn owls. If the increment in the 2 kHz component is balanced by decrementing the four flanking bands in amplitude, increment detection thresholds are not affected. The data suggest that the barn owls used information from simultaneous spectral comparison across different frequency channels to detect spectral changes in multi-component noise signals rather than sequential comparison of overall stimulus levels.

Preserved gain control for luminance contrast during binocular rivalry suppression

Binocular rivalry elevates contrast increment thresholds for the detection of a transient stimulus presented to the suppressed eye, while thresholds measured during dominance are identical to those during monocular viewing (e.g. [Wales, R., & Fox, R. (1970). Increment detection thresholds during binocular rivalry suppression. Perception and Psychophysics, 8, 90–94]). It is well established that contrast increment thresholds depend on reference (pedestal) contrast. With high contrasts, increment thresholds increase with pedestal contrast, reflecting a gain control with sigmoidal non-linearity. We examined how this gain control mechanism operates during binocular rivalry (i.e., with and without perception of a pedestal mask). Subjects viewed a horizontal sine-wave grating (steady pedestal) and a radial checkerboard dichoptically. When the grating achieved a pre-specified phenomenal state (dominance or suppressed), subjects initiated the transient presentation (500-ms Gaussian pulse) of a contrast increment of the same spatial frequency. The pulse appeared in either the upper or lower half of the pedestal. Subjects indicated which half of the pedestal contained the pulse. Contrast increment thresholds were measured using a staircase method with various pedestal contrasts, which yielded threshold versus contrast (TvC) functions during dominance and suppression. The measured thresholds were reliably higher during suppression, but the rising slopes of TvC functions did not differ significantly between dominance and suppression (i.e., constant upward shift of TvC function). A control experiment demonstrated that the TvC function during dominance was identical to that during non-rivalry, monocular viewing. Evidently, the contrast gain control for transient luminance increment does not require the perception of pedestal contrast.

Preserved gain control for luminance contrast during binocular rivalry suppression

Binocular rivalry elevates contrast increment thresholds for the detection of a transient stimulus presented to the suppressed eye, while thresholds measured during dominance are identical to those during monocular viewing (e.g. [Wales, R., & Fox, R. (1970). Increment detection thresholds during binocular rivalry suppression. Perception and Psychophysics, 8, 90-94]). It is well established that contrast increment thresholds depend on reference (pedestal) contrast. With high contrasts, increment thresholds increase with pedestal contrast, reflecting a gain control with sigmoidal non-linearity. We examined how this gain control mechanism operates during binocular rivalry (i.e., with and without perception of a pedestal mask). Subjects viewed a horizontal sine-wave grating (steady pedestal) and a radial checkerboard dichoptically. When the grating achieved a pre-specified phenomenal state (dominance or suppressed), subjects initiated the transient presentation (500-ms Gaussian pulse) of a contrast increment of the same spatial frequency. The pulse appeared in either the upper or lower half of the pedestal. Subjects indicated which half of the pedestal contained the pulse. Contrast increment thresholds were measured using a staircase method with various pedestal contrasts, which yielded threshold versus contrast (TvC) functions during dominance and suppression. The measured thresholds were reliably higher during suppression, but the rising slopes of TvC functions did not differ significantly between dominance and suppression (i.e., constant upward shift of TvC function). A control experiment demonstrated that the TvC function during dominance was identical to that during non-rivalry, monocular viewing. Evidently, the contrast gain control for transient luminance increment does not require the perception of pedestal contrast.

Effect of noise on the detection of intensity increments

The detection of an increment in a longer duration tone is often used as a measure of intensity resolution. Many studies of increment detection have used background noise, but few have varied the level of the longer duration tone relative to the noise or have compared results obtained with or without the noise. To explore this space in more detail, thresholds were obtained by adaptive tracking from four subjects for detection of a 50-ms increment in a 350-ms, 4000-Hz tone presented in quiet or in broadband noise of 0, 10 and 20 dB spectrum level. Tone levels ranged from 15 to 75 dB SPL in quiet and from approximately 0 to 30 dB above the tone’s detection threshold in the noise. Increment detection thresholds expressed as values of the difference in overall level of the tone resulting from addition of the increment increase as tone sensation levels decrease and are greater in noise than in quiet, but increase only slightly as a function of noise level. The data are well fitted by a model that assumes a specific form of nonlinearity motivated by loudness-matching data. [Work supported by NIDCD.]

Detection of an increment in a single-frequency component of a noise background as a function of increment frequency and duration

Increment detection thresholds for a single-frequency component were measured over a range of increment frequencies (250–6000 Hz) and durations (T=10–500 ms) in a 500-ms, 6000-Hz-wide noise. The noise spectrum level was either constant (N0=40 dB) or randomly varied (between N0=20 and 40 dB) from interval to interval. Preliminary results reveal performance for each increment frequency to be similar for the fixed- and random-level conditions. Detection thresholds for T=10 ms are largely independent of frequency and correspond to S-N0 values of 17–18 dB, whereas corresponding S-N0 values measured for long duration increments increase at a rate of 3 dB/oct for increment frequencies between 500 and 4000 Hz. The latter finding is consistent with changes in the critical ratio. This ratio is assumed to be based on an absolute energy cue, which is inconsistent in the random-level condition. Temporal integration (TI) functions fitted to the normalized detection data reveal less integration with increasing increment frequency from 500 to 4000 Hz. When the detection results are corrected for the apparent ‘‘critical ratio’’ effect, the TI functions are largely independent of increment frequency. [Work supported by ONR.]

Increment detection of bandlimited noises in the chinchilla

A positive reinforcement, adaptive tracking procedure was used to study the intensity discrimination abilities of six chinchillas to noise signals. Increment detection thresholds were obtained using a two-down, one-up tracking rule. The effect of overall noise masker level and the effect of noise bandwidth on increment detection thresholds were studied. The continuous noise masker and the signal increment had equal bandwidths. Increment detection thresholds are independent of overall level for wideband noise; the asymtotic DL for wideband noise is 1.334 dB. In addition, increment detection thresholds decrease as the bandwidth of the noise increases. The observed slope of the bandwidth function for the chinchilla is independent of overall level and is around − 2.8 dB/decade. The slope of the bandwidth function obtained for the chinchilla is similar to values reported for human subjects under similar conditions, but is less than the slope predicted by the ideal energy detector model.

Psychophysical detection and pain ratings of incremental thermal stimuli: A comparison with nociceptor responses in humans

The capacity of humans to detect and scale the magnitude of pain elicited by small increments in temperature, delivered by a contact thermal stimulator to localized areas of the arm or leg, was measured on non-painful and painful adaption temperatures. Subjects continuously rated the magnitude of any pain sensation elicited by heat increments superimposed on base temperatures of 38, 44, 47 or 48 °C. Detection threshold was also measured using a two-alternative forced choice method. The increment detection thresholds were lower for a continuously painful base of 47 °C than for a non-painful base of 38 °C in normal skin, and likewise were lower for a base of 38 °C following hyperalgesia induced by a mild burn. Incremental pain thresholds were nearly equal to detection thresholds on the base of 47 °C. The sensitivity with which subjects could scale the magnitude of pain was 2–7 times better for increments delivered on a 48 °C as opposed to a 38 °C base. Evoked responses in 6 single C-fiber mechanoheat nociceptive afferents (CMHs) were recorded percutaneously from the peroneal nerves of 3 humans, who were simultaneously judging pain magnitude. For a base of 38 °C, both the pain and the neural response thresholds were an order of magnitude higher than corresponding thresholds on a base of 48 °C. For a base of 47 °C, response thresholds of the CMHs ranged from 0.1 to 0.5 °C and were comparable to detection thresholds of 0.1 to 0.3 °C. The sensitivity with which most nociceptors could signal increment size was 3–4 times better on a 48 °C than a 38 °C base. Incremental pain sensitivity was not altered by a compression block of activity in myelinated afferents that eliminated the sense of cool and touch. Thus, activity in unmyelinated fibers alone could account for the sensitivity to incremental thermal stimuli that were superimposed on a painful base temperature. Further, it is likely that CMH nociceptors alone could provide the peripheral information necessary to detect and to make magnitude judgments of pain elicited by these stimuli.

On the inhibitory nature of binocular rivalry suppression.

During binocular rivalry the average duration of a suppression phase depends on the stimulus strength (e.g., contrast) of the input to the suppressed eye. To determine if a similar relationship exists between stimulus strength and the inhibitory effect of suppression on test probe detectability, a series of experiments was performed. Using two-alternative forced-choice procedures, increment detection thresholds were measured during phases of dominance and suppression. Results from three trained observers show that detection performance is significantly impaired during suppression by an amount that is independent of any difference in contrast between the rivalrous stimuli. These data indicate that the magnitude of the inhibitory effect of suppression is governed by a mechanism other than that which determines suppression duration.

Increment detection thresholds during binocular rivalry suppression

In two experiments, two-choice forced-choice duration thresholds for increment test flashes were estimated during phases of rivalry suppression and nonsuppression and for a nonrivalry monocular control condition. In both experiments thresholds of both eyes of each S were measured and, to maximize correct detections, feedback was given after every trial and Ss were relieved of the task of continually reporting changes in rivalry phases. Results of both experiments support the conclusion that suppression constitutes an elevation in threshold, on the order of .5 log units relative to thresholds found during nonsuppression and monocular conditions. These data, in concert with others, reinforce the general conclusion that rivalry suppression is an inhibitory state that nonselectively attenuates all classes of inputs falling within the spatial boundaries of the suppressed target.